After upgrading from ITMS 8.6 GA to 8.7.1, when trying to delete a task from the Task Status window, the task does not delete. However, the logs indicate that the tasks are being removed.
ITMS 8.7.1
This issue was fixed in ITMS 8.7.2 and is documented in the Release Notes as there is now a new Symantec Management Console feature, "Maximum time period to keep the task instances/summaries" that is now available in the "Clean up Task Data" setting page.
What's New in This Release (ITMS 8.7.2)